An intake unit, such as an electronic throttle device, has been conventionally known as an example of the valve unit. The electronic throttle device is adapted to control an operation of an electric motor in accordance with the amount of pushing operation of a gas pedal, thereby to control a throttle opening degree, which corresponds to a valve opening degree of a throttle valve, to a target value.
In such an electronic throttle device, a structure of restricting icing of the throttle valve and a shaft supporting the throttle valve has been proposed, for example, in JP-A-2005-290994, JP-B2-3787861 corresponding to U.S. Pat. No. 5,704,335, and JP-B2-4013249 corresponding to U.S. Pat. No. 6,814,051.
FIGS. 5 and 6 show an example of an electronic throttle device having the icing restricting structure. As shown in FIGS. 5 and 6, the throttle device has a throttle body providing a throttle bore 101 therein through which intake air flows. The throttle body has a double-tube structure including an inner tube 104 and an outer tube 105, and forms annular grooves 111, 112 between the inner tube 104 and the outer tube 105. The annular grooves 111, 112 can capture water content flowing from an upstream location or a downstream location of the throttle body with respect to a flow of the intake air along an inner surface of an intake air passage, thereby to restrict a throttle valve 102 and a shaft 103 supporting the throttle valve 102 from being iced due to the water content.
The throttle body has a separation wall 113 between the inner tube 104 and the outer tube 105 to separate the annular groove 111 from the annular groove 112. The throttle body has a first bearing portion 114 and a second bearing portion 115 to support a first end and a second end of the shaft 103, respectively. Further, a bearing, such as a ball bearing 116, is disposed between the second end of the shaft 103 and the second bearing portion 115.
The above structure is effective in a case where the throttle device is mounted in a vehicle in a side-draft manner such that an axis of the throttle bore 101 extends in a horizontal direction, which is perpendicular to an up and down direction of the vehicle. In this case, water is captured in the annular grooves 111, 112. The captured water is collected at the lowest locations in the annular grooves 111, 112. Further, in a case where the throttle device is mounted such that the shaft 103 extends in the horizontal direction, the water flowing over from the annular grooves 111, 112 can be drawn to combustion chambers of the engine via portions that are the furthest from the bearing portions 114, 115 of the throttle body.
In such a throttle device, if water is applied to the vicinities of the bearing portions 114, 115, the water is likely to enter clearances between the ends of the shaft 103 and the bearing portions 114, 115 and/or in the bearing 116 and permeate therein due to capillarity.
If an ambient temperature drops lower below freezing after the engine is stopped, the water is frozen in the clearances between the ends of the shaft 103 and the bearing portions 114, 115 and/or in the bearing 116, and thus the throttle valve 102 and the shaft 103 are iced. If the engine is started in the condition where the throttle valve 102 and the shaft 103 are iced, malfunctions, such as an inoperative condition of the valve 102 and a shaft lock, occur.
That is, the icing of the throttle valve 102 and the shaft 103 results in an occurrence of icing torque. When the electronic throttle device mounted in the side-draft manner, however, the occurrence of such icing can be reduced.
Also, it is proposed to mount the throttle device in a down-draft manner such that the intake air flows in a downward direction or in an up-draft manner such that the intake air flows in an upward direction. FIG. 7 shows an example of the throttle device mounted in the down-draft manner. The longitudinal axis of the throttle bore 101 extends in a vertical direction, such as in the up and down direction of the vehicle.
In the throttle device mounted in the down-draft or up-draft manner, water can be temporarily stored in the annular groove 111, which is open in an upward direction. However, it is uncertain from which position the water overflows in the top end of the inner tube 104 with respect to a circumferential direction. The water may reach a bearing portion 117 of the throttle body along an inner surface of the inner tube 104. In the example shown in FIG. 7, a bearing 119 is disposed between the shaft 103 and the bearing 117.
In the throttle device mounted in the down-draft or up-draft manner, it is further proposed to incline the annular groove 111 with respect to the horizontal direction of the vehicle, such as a vehicle front and rear direction or a vehicle right and left direction, as shown in FIG. 8. In this case, the water temporarily stored in the annular groove 111 can overflow from the annular groove 111 through the lowest position of the upper end of the inner tube 104. Such a throttle device is, for example, described in JP-A-2002-221051. In JP-A-2002-221051, it is proposed to form a notch (not shown) at the lowest position of the upper end of the inner tube 104 such that the water can be discharged from the annular groove 111 through the notch.
In the above throttle device, however, the upper end of the inner tube 104 is inclined, and the bottom of the annular groove 111 is also inclined. Therefore, the amount of water stored in the annular groove 111 is smaller than the amount of water stored in the annular groove 111 having a horizontal bottom as shown in FIG. 7. Also, it is necessary to care the position of the notch such that the notch is located at the lowest position in the upper end of the inner tube 104 when the throttle body is assembled.